Visual lightning detection by the human eye is excellent at night but very poor in daylight. During the day, cloud-to-ground (CG) lightning can be seen against a dark background, but it is difficult to see against a bright background. Further, intracloud (IC) flashes, the best indicators of thunderstorm development, occur 5 to 50 times as frequently as CG flashes, and are almost never seen in daylight. Experience indicates that optical signals from IC lightning are usually detected 10 to 15 minutes before any CG lightning is reported. Thus the ability to detect IC lightning is not only advantageous for monitoring thunderstorm development and intensity, but it can provide earlier warning than systems which only detect CG lightning.